U.S. Pat. No. 5,106,270 to Goettel et al., and assigned to the assignee of the present invention, shows an integral compressor and aftercooler that is extremely efficient in cooling hot, high pressure discharge air from a compressor. When the compressor is operating under a heavy duty cycle the air temperature is reduced to within 20° of ambient temperature. If the compressor is running in a start/stop manner under a light duty cycle, the temperatures of the heated gases from the compressor can be reduced to temperatures within 5° of ambient. With such efficiency it is quite possible for moisture contained in the aftercooler or in the discharge air from the aftercooler to freeze when operating under freezing conditions.